The characteristic parameters specified in the data sheet of a semiconductor memory, for example of a DRAM (—Dynamic Random Access Memory) semiconductor memory, are only guaranteed by the manufacturer if the memory chip is operated within specified limits of operating parameters. Such operating parameters include, e.g., the permissible supply voltage range in which the semiconductor memory is permitted to be operated. If a higher voltage than the voltage specified in the data sheet is applied, this may result in the destruction of components on the chip, which leads to the failure of the semiconductor memory. Further operating parameters specified by the manufacturer are for example the permissible ambient temperature range in which proper functioning of the semiconductor memory is guaranteed, and also the permissible clock frequencies at which the semiconductor memory is to be operated.
If devices fail when they are in the customer's possession, they are generally returned to the manufacturer in order for the manufacturer to determine the reason for the failure in the context of a fault analysis. In this case, it is desirable to ascertain whether the failure of the semiconductor memory is attributable to deficiencies in the manufacturer's fabrication process or to the memory chip being operated by the customer in a manner not conforming to the specification. Operating a memory chip in a manner not conforming to the specification includes, for example, overclocking a DRAM, operating the DRAM at impermissibly high voltages or operating the DRAM at excessively high or excessively low temperatures. However, the fault pattern of a device often does not permit unambiguous conclusions about the cause of the failure. Therefore, it would be desirable for the manufacturer to have reliable information available about the operating conditions of the device in the customer's possession.
Furthermore, knowledge of operating parameters of a semiconductor memory can advantageously be used for optimizing modules or else further peripherals of the semiconductor memory. The distribution of the temperature loading of the individual chips on a module is predefined by system variables such as, for example, by the position of a fan on the main circuit board of a computer. If it is possible to determine the distribution of the maximum temperature loading on a module of, for example, a DIMM, then this information can be used to optimize the position of specific components on the module, so that, by way of example, one device is not blocked from the air stream of a fan by another device.
Knowledge of operating parameters under the influence of which a device has failed furthermore enables the test range, for example the temperature range in which devices are exposed to high or low temperatures, to be determined in a manner adapted to the application. By way of example, the intended function of a semiconductor memory according to the data sheet is guaranteed only in a certain temperature range. In the manufacturer's test bed, the devices are generally exposed to higher or lower temperatures and then subjected to a functional test again. By testing the device with a specific temperature margin above or below the specified temperature range, this overcritical testing permits the manufacturer a certain safeguard against failures of the device on account of temperature loading. If the manufacturer knows the actual temperatures to which the device is exposed in the case of the respective customer applications, the temperature range to be tested can be determined more precisely on the part of the manufacturer and be better adapted to the customer's application.